Hope we are talking about true Push Presses. Where the bar will rest more on the heel of the hands (thumbless grip) rather than on the pads/palm of the hands. With the bar resting on the heels of the hand the pressing force (push) is more inline with the wrist/forearm, giving more direct power to the lift. With a regular pressing grip, it is not and there may be too much strain on the wrist themselves, when heavier weights are used. This will also apply to the bench press, for some men prefer a thumbless grip.(the BP has gone up for some men with this style...Caution, a good spotter(s) may be required).
As a general rule, you will use more weight in the push press. There is also a slight knee motion with that exercise. Most men will find that they get a better, more solid position on the push press, when it's off the rack/stands, etc.. The Jerk press, which a lot of football players include in workouts, is that much more of a knee and dip action than even the push press.
One of the better workouts of overhead presses is starting with the regular press (somewhat strict) for one or two sets. Then the next one or two sets, adding weight, do Push Presses. And the final one or two sets, adding weight, do jerk presses. And if you wish (though not really needed) drop the weigh back down to the original weight used on the regular press and see how many reps you can do. All these are to be done off a power Rack or a version of the same. Outstanding pump is included, when working out this way, for the upper body. You should be buying new shirts in 1 or 2 month if doing these pressing styles with serious intent.
The Bradford Press (Jim Bradford..old time Olympic lifter?), as LatsMcGree suggest, is also a very good exercise for the whole shoulder girdle. Though not meant for every one. Really need a complete warm-up/stretch before attempting this one. It's a combo of front and behind the neck pressing styles in one exercise.
Of course if you want a complete shoulder/trap workout than do cleans (off the floor) and jerk presses. Two or three sets should do it for anyone. 8-12 reps for BB'ing. 4-6 for power as a general rule. Good Luck.
